Digital display systems temporally modulate light to create images. A typical digital display system uses a digital micromirror device (DMD) to selectively reflect portions of an incident beam of light to an image plane. The DMD is an array of mirrors that are rotated in one of two directions about a torsion hinge. In the first position (on), light incident the mirror is reflected towards an image plane, typically by way of a projection lens. The light reaching the image plane forms a bright spot on the image plane representing a picture element, or pixel. When the mirror is rotated in the opposite direction to a second position (off), the light reflected by the mirror does not reach the image plane and the pixel corresponding to the mirror in the off position is dark.
Intermediate intensities are created by rapidly cycling the mirror on and off. The amount of light reflected to the image plane is a function of the duty cycle of the mirror. The human eye, or other integrator such as a photosensitive medium located at the image plane, integrates the amount of light reaching each pixel over a period of time and creates the impression of an intermediate pixel brightness. Color images are formed by superimposing three simultaneously or sequentially-generated single-color images.
Although the duty cycle of the mirror controls the time during which light is reflected to the image plane, other factors may upset the relationship between pixel intensity and duty cycle. What is needed is a more efficient method of controlling pixel intensity in pulse-width modulated display systems.